Diaphragm valves, comprising a flexible diaphragm mounted on a matching valve base, are used in many fields as one way valves. Typically, the diaphragm is positioned over one or more apertures in the valve base and is secured in such a way that a relative decrease in pressure on the diaphragm side of the base causes the diaphragm to lift away from the base, thereby opening the apertures whereas a relative increase in pressure causes the diaphragm to be pressed against the base, thereby closing the apertures. Diaphragm valves of that type are used, for example, in the field of personal respiratory protection devices where they may be employed as both inhalation and exhalation valves.
In one known type of respirator, in which diaphragm valves are used as inhalation valves, the valve diaphragms are mounted on respective filter assemblies through which air enters the respirator when the wearer breathes in. The filter assemblies are located in the cheek areas of the face piece of the respirator and incorporate a filter material through which inhaled air must pass before it reaches the inhalation valve. The filter material is chosen having regard to the intended use of the respirator and may serve to remove particulate material and/or noxious gases or vapours from the inhaled air. The face piece also incorporates, in the nose and mouth area, an exhalation valve through which air leaves the respirator when the wearer breathes out. The exhalation valve is designed to close when the wearer breathes in so that air enters the respirator through the inhalation valves and must pass through the filter material. Likewise, the inhalation valves are designed to close when the wearer breathes out so that exhaled air leaves the respirator through the exhalation valve and does not contact the filter material.
A filter assembly of a respirator of that type may comprise a moulded plastics casing in which the filter material is contained, the casing being formed with at least one intake aperture on the side adjacent the interior of the face piece of the respirator. The flexible diaphragm of the inhalation valve is secured over the aperture(s) on the inside of the face piece in such a way that, when the wearer breathes in, the diaphragm lifts away from the aperture(s) to allow the entry of air to the respirator. When the wearer breathes out, however, the diaphragm is pushed against the filter assembly so that it covers over and seals the intake aperture(s). To facilitate respirator manufacture, it is clearly desirable to be able to secure the diaphragm to the filter assembly by an automated process.
One procedure which is used for securing inhalation diaphragms to respirator filter assemblies is ultrasonic welding. To that end, the moulded plastics casing of a filter assembly is formed with at least one upstanding post which, when the inhalation diaphragm is positioned on the filter assembly, projects through an aperture in the diaphragm. The end of the post is then softened and enlarged using ultrasonic energy to form a head which holds the diaphragm in position on the filter assembly. Although that procedure works well, it must be carried out by trained operators and is, therefore, comparatively expensive. It also tends to be more time consuming than other parts of the manufacturing process and, consequently, limits the efficiency of respirator production.
As an alternative to the use of posts which are formed integrally with the casings of the filter assemblies, separate fixing pins are available which comprise an enlarged head for retaining the pin in the casing and a centrally-split stem which is first inserted through an aperture in the diaphragm valve and is then spread open to hold the diaphragm in position. The use of such separate fixing pins eliminates the need to use ultrasonic welding techniques but is more complex because it involves a greater number of components.